The present invention relates to a temperature stable photochromic composite. More particularly, the present invention relates to a photochromic composite material wherein the active photochromic component comprises spirooxazines and the polymeric host comprises copolymers of poly(vinyl alcohol) and poly(vinyl acetate).
Compounds which undergo reversible photo-induced color changes are termed photochromic compounds. When subjected to ultraviolet or visible light irradiation, these photochromic compounds change their light transmission properties and hence undergo color changes. Photochromic compounds subsequently revert to their original color state when they are subjected to a different wavelength of radiation or when the initial light source is removed.
The photochromism of spirooxazine compounds is well known and disclosed, for example, in U.S. Pat. Nos. 3,562,172 and 3,578,602. These compounds are spirooxazine derivatives with substitutions in the indoline portion of the molecule. U.S. Pat. Nos. 4,215,010 and 4,342,668 disclose spirooxazine derivative compounds with substitution in the naphthalene part of the molecule in addition to substitution in the indoline part of the molecule. The spirooxazine derivative compounds in the latter two patents exhibit an enhanced photocolorability when compared to the spirooxazine derivative compounds disclosed in U.S. Pat. Nos. 3,562,172 and 3,578,602. Other spirooxazine compounds having different ring systems have been reported. For example, European Patent Application EP No. 245,202, U.S. Pat. No. 4,637,698, Japan Kokai Tokkyo Koho JP No. 62 72,778 and JP No. 62-164,685 disclose spirooxazine compounds in which the naphthalene part of the molecule is replaced by benzene, quinoline, anthracene and phenanthrene, respectively.
Commercial applications for photochromic compositions of the type hereinabove described include sunglasses, ophthalmic lenses, ski goggles, window coatings and the like. In these applications, the Photochromic compositions are incorporated into a plastic host material such as cellulose acetate butyrate, poly(vinyl butyral) and the like.
The composition of the plastic host influences the photocolorability of the spirooxazine compounds. Unfortunately, it is well known that regardless of how the compositions of the plastic hosts are varied, the photocolorability of plastic articles made from most common commercially available plastics show a strong temperature dependence. Namely, photocolorability of the plastic article decreases as the temperature increases. At temperatures greater then 60.degree.-70.degree. F., the photocolorability is substantially decreased. This temperature dependence is highly undesirable and acts to limit the successful utilization of these photochromic compounds in many applications.